Chemistry Reference
In-Depth Information
3.2.5
Polyethylenimines (PEIs) with Adducts that Self-assemble into Catalytic Moieties
Metal ions participate in the catalytic action of many enzymes. In the hydrolysis of
peptide bonds of proteins and phosphodiester bonds of RNA and DNA, for example,
metal ions play various catalytic roles, acting as Lewis acid catalysts [39]. 2-Hydroxy-
propyl-p-nitrophenylphosphate (HPNPP) has been widely employed as an activated
analogue of RNA. Transesterification of HPNPP is effectively catalyzed by two or
more metal ions acting together [40, 41]. This catalytic action has been explained
in terms of activation of the two phosphoryl-oxygen bonds and general base assistance
for the intramolecular attack of the hydroxyl group (
4
) [41].
HPNPP
4
As rationally designed multinuclear catalysts for transesterification of HPNPP, me-
tal complexes such as
5
have been designed [42]. By random attachment of lauryl
groups and Ni(
II
) complexes of terpyridine (TP) to PEI (
6
) we have synthesized a poly-
mer that has much higher catalytic activity than
5
for the same reaction [43]. The con-
tents of the pendant groups were varied in several combinations, and the best catalyst
([Ni(
II
)TP]
5
Lau
12
PEI) contained 5 residue mol% Ni(
II
)TP and 12 residue mol% lauryl
group.
The calix[4]arene-based binuclear Zn(
II
) complex (
5
) manifests optimum activity at
pH 7.4. The maximum k
o
attainable by
5
is 1.0
10
-3
s
-1
regardless of pH or C
o
. Much
higher k
o
s were observed with [Ni(
II
)TP]
5
Lau
12
PEI (Figure 3.6).
5
